In the manufacture of printing inks, efforts are continuously made to develop new and improved polyamide compositions useful as pigment binders in inks for printing a variety of substrates. In particular demand are those inks which can be printed or laminated on polyolefin substrates such as polyethylene. These inks must possess a number of qualities to be commercially useful, including good ethanol solubility and reducibility, and good viscosity stability in solution among others.
Polyamides comprising dimerized fatty acids are known to be useful in the manufacture of printing inks and in adhesive applications. According to U.S. Pat. No. 3,377,303, polyamide compositions including a piperazine or dipiperdyl type diamine component are disclosed as suitable for hot melt binding. Good adhesion to vinyl substrates by these polyamide compositions are shown, however such adhesive compositions are generally poorly soluble in alcohol and possess other properties suitable for adhesion but generally unsuited for applications as an ink resin binder.
U.S. Pat. No. 3,652,469 teaches polymeric fatty acid polyamide resins obtained by reacting an acid mixture of a polymeric fatty acid and a low aliphatic monocarboxylic acid with an amine mixture of an alkylene diamine and a polyhexamethylene polyamine. The resins are disclosed as being particularly useful in flexographic ink. Although these products have good solubility in alcohol achieved in part through the condensation of a monobasic acid as part of the acid component, the resultant lower molecular weight product results in less desirable tensile properties. Similarly, Re. 28,533 discloses synthetic polyamides prepared by condensing a monocarboxylic acid, diamine and dimerized fatty acid. Again, the lower molecular weight compositions obtained by condensing inter alia a monocarboxylic acid achieves ethanol solubility generally at the expense of tensile properties. According to U.S. Pat. No. 4,571,267, alcohol-soluble polyamides and printing inks are disclosed prepared by condensing an acid component of dimerized fatty acids, at least one aliphatic unbranched monocarboxylic acid and at least one aliphatic branched monocarboxylic acid with ethylenediamine and hexamethylenediamine as the amine component.
Thus there is a need for polyamide resin compositions for use as laminating ink resin binders which possess desirable properties such as good ethanol solubility and reducibility, good viscosity stability in solution and good softening points.